An improved test of time dilation in special relativity has been performed using laser spectroscopy on fast ions at the heavy-ion storage-ring TSR in Heidelberg. The Doppler-shifted frequencies of a two-level transition in 7Li+ ions at v=0.064c have been measured in the forward and backward direction to an accuracy of Deltanu/nu=1 x 10(-9) using collinear saturation spectroscopy. The result confirms the relativistic Doppler formula and sets a new limit of 2.2 x 10(-7) for deviations from the time dilation factor gamma(SR)=(1-v2/c2)(-1/2).

Radiative recombination (inverse photoionization) is believed to be well understood since the beginning of quantum mechanics. Still, modern experiments consistently reveal excess recombination rates at very low electron-ion center-of-mass energies. In a detailed study on recombination of F6+ and C6+ ions with magnetically guided electrons we explored the yet unexplained rate enhancement, its dependence on the magnetic field B, the electron density n(e), and the beam temperatures T( perpendicular) and T( ||). The excess scales as T(-1/2)( perpendicular) and, surprisingly, as T(-1/2)( ||), increases strongly with B, and is insensitive to n(e). This puts strong constraints on explanations of the enhancement.

The vibrational relaxation of H 3 ϩ molecules from a conventional plasma ion source is studied performing Coulomb explosion imaging on the ions extracted from a storage ring after variable times of storage. Storage for 2 s is found sufficient for radiative relaxation of the breathing excitation and the fragment velocity distribution in the breathing coordinate then agrees well with simulations based on the calculated ground-state wave function. The radiative decay of the two lowest pure breathing levels (1,0 0 ) and (2,0 0 ) is seen to be considerably faster than expected from rotationless calculations. Assuming a high rotational excitation of the H 3 ϩ ions, as suggested already in earlier experiments, the theoretical transition probabilities of the University College London line list for H 3 ϩ ͓L. Neale, S. Miller, and J. Tennyson, Astrophys. J. 464, 516 ͑1996͔͒ can explain the increase of the vibrational cooling rates and reproduce the observed decay curve for the lowest breathing-excited level, confirming the absolute transition probabilities of these line tables. The observations give evidence for a quasistable population of high-lying rotational levels in the stored ion beam, relevant for the interpretation of storage ring measurements on the rate coefficients for dissociative recombination of H 3 ϩ ions with low-energy electrons.

Fragmentation patterns for dissociative recombination of the triatomic hydrogen molecular ion H(3)(+) in the vibrational ground state have been measured using the storage ring technique and molecular fragment imaging. A broad distribution of vibrational states in the H(2) fragment after two-body dissociation and a large predominance of nearly linear momentum geometries after three-body dissociation are found. The fragmentation results are directly contrasted with Coulomb explosion imaging data on the initial H(3)(+) geometry, compared to existing wave-packet calculations, and considered in the light of a simple physical picture.

The breakup dynamics of H 3 ϩ and D 3 ϩ following dissociative recombination is studied using the combination of two-dimensional imaging and storage ring techniques. The vibrational distributions of the molecular H 2 and D 2 fragments produced in the two body fragmentation channel were measured, as well as the kinematical correlation between the hydrogen or deuterium atoms produced in the three body channel. For the latter, we find predominantly linear dissociation geometries. The data also show that the initial molecular ions H 3 ϩ and D 3 ϩ , which were stored and electron cooled for up to 40 s prior to recombination, are still rotationally hot.